Cell Membranes Contents: Structure: the basics Fluid mosaic model/freeze fracture technique Membrane fluidity Membrane fluidity and cholesterol The Basics? The plasma membrane separates the living cell from its surroundings Phospholipids make up the majority of the bilayer Phospholipids consists of a hydrophilic phosphate head and two hydrophobic fatty acid tails Phospholipids are amphipathic molecules: containing both a hydrophilic and hydrophobic region The plasma membrane is described by the fluid mosaic model: The membrane is fluid with a variety of ?mosaic? proteins embedded in it The plasma membrane is selectively permeable: Small fat soluble (hydrophobic ? non polar) molecules, can enter the cell through the lipid bilayer (this occurs rapidly) e.g. hydrocarbons